Time Machine says your backup disk is full

Why it happens

A backup disk holds a full copy of your Mac plus older versions of files that changed. When space runs out, Time Machine removes the oldest backups first. If your Mac now holds more than the disk can fit, or other files share the disk, removing old backups can't free enough room, and Time Machine tells you.

How to fix it

1. Open the Apple menu, choose System Settings, click General in the sidebar, then Time Machine.

2. Click Options… to see what's left out of your backups.

   General›Time Machine›Options…

3. Under Exclude from Backups, click the add button (+) and choose big folders you don't need backed up, such as Downloads or a folder of videos you already keep elsewhere. Click Done.

4. Choose Back Up Now from the Time Machine icon in the menu bar, and see if the backup finishes this time.

   Menu bar›Time Machine›Back Up Now

The Time Machine page is the same on macOS 26 and 27. On macOS 27 the button for a new disk reads Add Backup Disk… with three dots.

Still not fixed?

1. Look at what else is on the backup disk. Files you saved there yourself take space Time Machine can't use. Move them to another drive.

2. Clear out your Mac too. Big files you don't need still get backed up, so find and remove them in General > Storage.

   General›Storage

3. If you back up to a network disk, it may have a size limit set for backups. Raising that limit on the network disk gives Time Machine more room.

4. Get a bigger disk. Aim for at least twice your Mac's storage so there's room for history. Add it with Add Backup Disk… in Time Machine settings.

   macOS 26 Tahoe General›Time Machine›Add Backup Disk

   macOS 27 Golden Gate General›Time Machine›Add Backup Disk…

5. If the disk still fills up with nothing else on it, run First Aid on it in Disk Utility. If First Aid finds errors it can't repair, the drive may be failing, which is a hardware problem: replace it, or have its maker or a repair shop check it while it's under warranty.

   Disk Utility›First Aid